1. Field of the Invention
The present invention relates to an ultrasonic diagnostic system in which a tomographic image of the subject according to the ultrasounds is obtained, and more particularly to an ultrasonic diagnostic system which incorporates therein the technique for extracting the outline of a tissue within the subject.
2. Description of the Related Art
Hitherto, there has been used an ultrasonic diagnostic system in which ultrasonic beams are transmitted into the inside of the subject and the ultrasounds reflected from the inside of the subject are received to obtain received signals, so that a tomographic image of the subject is displayed on the basis of the received signals for diagnosis of diseases of the viscera and the like of the human body. Recently, in order to more facilitate the diagnosis of diseases, it is required that the outline of the tissue appearing on the tomographic image, for example, the left ventricle of the heart, is extracted and displayed, or area of a domain surrounded by such an outline and volume of the tissue estimated from the outline are displayed.
To extract the outline, simply, as shown in FIG. 45, an operator may trace, with for example a light-pen 2, the tomographic image displayed on a display unit 1 along the outline of a desired tissue. Thus, it is possible to extract the outline through the locus of the light-pen 2.
Further, as shown in FIG. 46, there has been proposed a technique in which a domain 3 is designated in such a manner that a desired tissue is surrounded using, for example, a track ball, a mouse or the like, and image data within the designated domain is binarized with a suitable threshold to extract an outline (Tosikazu Yagi, et al. "Measurement of sectional area of left ventricle and volume of left ventricle according to acoustic quantification method; Influence of set site for domain of concern", pp.517-518, Literature of No. 63 Meeting of Japan Ultrasonic Medical Institute, published on November, 1993).
However, according to the former involved in the method in which the outline is traced by a person, there is a need to carefully trace the tomographic image so as to prevent the locus by the light-pen or the like from being out of the outline. In addition, in case of the left ventricle which is the tissue of which an outline is to be obtained, there will be a need to repeatedly perform such a tracing operation for a lot of tomographic images over a pulse of movement of the heart in its entirety. This often involves inaccuracy in data lacking objectivity in spite of the fact that it is troublesome, and thus it is far from practical use.
Further, also in the later involved in the method in which an outlined domain 3 is designated and image data within the designated domain is binarized, thereby extracting an outline, there is a need to carefully perform the designation of the domain for each tomographic image, since the heart is always beating and repeats the expansion and contraction. For example, as shown in FIG. 46(A), if the inside of the domain 3 includes not only the left ventricle 4 but also the left atrium and the right ventricle, or as shown in FIG. 46(B), if a part of the left ventricle 4 is out of the domain 3, there will be evaluated erroneous values in both the area and the volume of the left ventricle 4. In order to avoid this problem, there is a need to carefully surround only the left ventricle 4 in its entirety through a manual work. Thus, the problem involving troublesomeness is not solved, while it is less troublesome than tracing the outline. Further, according to the method in which image data within the designated domain 3 is binarized to extract an outline, a luminance (the size of image data) is varied in accordance with the affect due to the noise and the like, and the place. Thus, it happens that a contour lacking a continuity as a two-dimensional image, or a contour forming no closed surface is extracted.
In view of the foregoing, it is an object of the present invention to provide an ultrasonic diagnostic system that are functionally capable of objectively extracting an outline of the tissue without a manual work, or with a simple manual work.
It is another object of the present invention to provide an ultrasonic diagnostic system having such a function that the mere input of outlines as to a small number of frames permits outlines as to a large number of frames to be extracted.